B4a / Side 1
How Plant Feed
Green plants make food during the process of photosynthesis.
Copy and complete the word equation, which summarises photosynthesis:
+ +
( Raw materials / reactants ) / ( Products )Copy and complete the diagram by filling in the empty boxes:
Where does the energy come from to make this reaction happen?
Plants have many coloured substances in their leafs known as pigments. The jobs of the pigments are to absorb light energy. The main pigment found in plant leafs is chlorophyll. Chlorophyll is found in chloroplasts, small structures found in most plant cells.
What colour do you think chlorophyll is?
KS4 Biology /B4a / Side 2
Plants make glucose first and then change this sugar into starch, which is stored in the leaf and other parts of the leaf.
Why can we use a starch test as evidence that photosynthesis has been happening?
Potatoes are full of starch. Potatoes are formed from the roots becoming swollen with starch. Does finding starch in potatoes show that photosynthesis has been happening in that part of the plant, explain your answer.
Make a list of all the variables (factors) that you think will affect the rate (how fast something happens) of photosynthesis and for each variable explain why you think changing it will affect the rate:
KS4 Biology /B4b / Side 1
Adaptations of a Leaf for Photosynthesis
The leaves are the main place where photosynthesis takes place on a plant.
They are well adapted (suited) to this job.
A. Some adaptations make the leaf good at ABSORBING LIGHT
Feature / Explanation1. The leaf stalks (petioles) bend throughout the day
2. Leaves are arranged in a mosaic pattern (spread out evenly around the stem)
3. Leaves are usually broad and flat
4. The mesophyll cells contain chloroplasts
5. The palisade mesophyll cells have most chloroplasts
6. Upper epidermis is thin and transparent
KS4 Biology /
B4b / Side 2
B. Some adaptations make the leaf good at GAS EXCHANGE
Feature / Explanation1. Leaves are thin
2. The waxy cuticle is penetrated by many stomata (plural of stoma)
3. There are air spaces between the spongy mesophyll cells
C. Some adaptations make the leaf good at TRANSPORT
Feature / Explanation1. Leaves have veins containing two types of transport pipes (xylem and phloem)
The diagram below is a plan diagram of the tissues found in a leaf:
KS4 Biology /B4b / Side 3
Complete the table below, give the name for each part and place a tick if you think that part is involved in photosynthesis; transport of water and glucose or gas exchange (more than one box may be ticked).
No. / Name / Photosynthesis / Transport of water and glucose / Gas exchange1.
2.
3.
4.
5.
6.
7.
KS4 Biology /
B4b / Side 4
Dicotyledon Leaf
Identify and label the following from the information given here.
Sha Tin College / Science Department - August 051. Cuticle (transparent layer on top of the leaf)
2. Upper epidermis (single layer of flat cells covering the top surface of the leaf)
3. Palisade layer of cells (layer of long cylindrical cells just under the upper epidermis)
4. Spongy mesophyll (layer of cells with air-spaces between them)
5. Stomata (pores on the underside of the leaf)
6. Guard cells (control the opening and closing of the stomatal pores)
7. Vascular bundle (contains conducting tissues)
8. Xylem (conducts water)
9. Phloem (conducts food)
Sha Tin College / Science Department - August 05KS4 Biology /
B4c / Side 1
Testing a Leaf for Starch
Diagram / Step / Reason/ Place a leaf into boiling water for about a minute
Turn off the Bunsen burner flame.
/ Put the leaf into a boiling tube containing ethanol. Put the boiling tube into the hot water. The ethanol will boil. Leave the tube for about 5 minutes.
/ Remove the leaf from the ethanol and wash it in the water.
/ Carefully spread the leaf out onto a white tile and then cover the leaf in brown iodine solution.
If starch is present what colour will the iodine solution turn?
If starch is present in the leaf, what does this indicate?
KS4 Biology /B4d / Side 1
Factors Needed for Photosynthesis
As you have seen previously a starch test can be used to detect if a plant has been carry out photosynthesis.
Is Chlorophyll needed for Photosynthesis?
A variegated plant has leafs that are a mixture of colours. The most common type has green and white leafs. Below is a diagram showing a variegated leaf:
/ Why is the green area green?Why is the white area white?
Take a variegated leaf that has been exposed to bright light for a few hours and perform a starch test on it. In the boxes below make labelled drawings of the leaf as it appeared before and after the starch test.
Before / AfterWhat can you conclude from your results?
KS4 Biology /B4d / Side 2
Is Carbon Dioxide needed for Photosynthesis?
Two plants of the same species were placed in the dark for 12 hours. A leaf was then tested for the presence of starch. The two plants were then set up as shown below:
Take a leaf from each plant and perform a starch test. Draw your results in the boxes below:
Leaf from plant with petri dish of water / Leaf from plant with petri dish of sodium hydroxideWhy must you start this experiment with two plants, which have been in the dark for 12 hours?
Why was a starch test done on a leaf before setting up the apparatus?
What was the job of the sodium hydroxide?
What can you conclude from your results?
KS4 Biology /B4d / Side 3
Is Light needed for Photosynthesis?
A plant was placed in the dark for 12 hours. A leaf was then tested for the presence of starch. Some of the leafs were set up as shown below and left in bright light for a few hours.
Take one of the leafs that have been set up as shown above and perform a starch test on it.
Draw your results in the box below:
What can you conclude from your results?
KS4 Biology /B4e / Side 1
Glucose is turned into Starch for Storage
When plants carry out photosynthesis they make glucose. Glucose molecules are quite small and they dissolve easily in water. If there was lots of glucose dissolved in the cytoplasm of a plant cell, how might this affect the cell? (Think back to unit B1)
If a plant makes lots of glucose molecules it turns them into starch. Starch is a very big molecule made up of lots of glucose molecules jointed together. Starch molecules do not dissolve in water and they are very compact so therefore take up less space than lots of individual glucose molecules.
As well as starch there are many other substances a plant can make from glucose. Glucose and starch belong to a group of chemicals called carbohydrates. Glucose can also be changed into other carbohydrates such as sucrose and cellulose.
Another important group of biological chemicals is fats. Glucose can be changed into fats / oils in plants.
Glucose can also be changed into a third group of biological chemicals called proteins. Proteins are important to plants, as they are needed for growth. However, to do this plants need to add nitrogen to the glucose. They get the nitrogen in the form of nitrates or ammonia salts from the soil.
KS4 Biology /B4e / Side 2
1. Give two reasons why it is better for a plant to store its glucose as starch?
2. Name all the carbohydrates that are mentioned in this passage.
3. Give the names of some plants that convert a lot of their glucose into fats / oils.
4. What element needs to be added to glucose to make proteins? Where do plants get this important element?
KS4 Biology /B4f / Side 1
Factors Affecting the Rate of Photosynthesis
Farmers who grow crops are interested in improving the quality of their crops and producing as much food as possible. Whether plants grow quickly or slowly is partly determined by the rate of photosynthesis ( How fast they carry out photosynthesis in a set amount of time ).
The rate of photosynthesis can be measured by looking out how quickly a plant produces oxygen in a set amount of time.
Label the apparatus shown below:
(Use the following words: Light source; oxygen bubble; Water plant; Water with sodium hydrogen carbonate)
How can this apparatus be used to measure the rate of photosynthesis?
Why is this method inaccurate?
How could you make the method more accurate?
KS4 Biology /B4f / Side 2
How could you change the following variables (factors) to see whether they affect the rate of photosynthesis?
Light intensity
Temperature
Carbon dioxide concentration
Wavelength of light
KS4 Biology /B4f / Side 3
Investigating the Rate of Photosynthesis
Plan an investigation to investigate how changing one of the following variables will affect the rate of photosynthesis:
· Light intensity
· Wavelength of light
· Carbon dioxide concentration
· Temperature
Your investigation will be presented as a poster and handed in for assessment.
Planning:
Make sure you have completed the following when planning your investigation:
· State what variable you are investigating
· Made a prediction about what you think will happen as that variable is changed (increased or decreased)
· Explained why you think you prediction is right
· Made up a list of the apparatus you will be using and drawn a diagram to show how it will be set up
· Explained how you are going to change your investigated variable
· Explained how you are going to make it a fair test by keeping all the other variables the same
· Drawn up a results table to record your results
After you have done your investigation:
Make sure you do the following:
· Plot a graph of your results, think carefully about what type graph you will be drawing and make sure that the variable that you controlled goes onto the x-axis and the variable that you measured on the y-axis. Remember to label axes with titles and units and to give your graph a title.
· Make a conclusion about what your results tell you. How does changing your variable affect the rate of photosynthesis
· Make an evaluation about your results. How would you improve the investigation if you had the chance to do it again?
·
KS4 Biology /B4g / Side 1
Limiting Factors in Photosynthesis
Light intensity, temperature, supplies of carbon dioxide and water together affect the rate at which plants make glucose by photosynthesis. They are the environmental factors that control or limit the rate of photosynthesis.
Look at the graph below:
It shows the results of an experiment to find the effect of increasing light intensity on the rate of photosynthesis.
Look at the start of curve A, what happens to the rate of photosynthesis as the light intensity is increased?
However, eventually there comes a point when the curve starts to flatten out and the rate of photosynthesis does not increase anymore however much you increase the light intensity. Why do you think that the rate of photosynthesis stops increasing at this point?
The answer could be that the rate of photosynthesis is going at its maximum speed or it could be that another factor other than light is stopping photosynthesis going any faster. Name some other factors that could be doing this:
One possibility could be carbon dioxide. How could you find out if it was carbon dioxide?
KS4 Biology /B4g / Side 2
Curve B shows what happens when the level of carbon dioxide is increased. What happens to the rate of photosynthesis?
However, even curve B eventually flattens out so what could the limiting factor now be?
A limiting factor is described as the factor, which is in shortest supply and so, will stop the reaction going any faster, it will limit the rate.
Question:
An investigation was carried out to compare the effects of different temperatures and different light intensities of white light on the rate of photosynthesis.
The results are shown in the graph below:
Describe how light intensity affects the rate of photosynthesis at 15°C.
KS4 Biology /B4g / Side 3
Explain why there is a difference when the investigation is carried out at 30°C.
A gardener in the New Territories wishes to grow broccoli in a heated and lit greenhouse during the winter. What could the gardener learn from the results in order to make sure that his bill from CLP power is not too high?
Sugars such as glucose are products of photosynthesis. These are the raw materials from which plants synthesise (make) other substances.
Name three other substances synthesised by a plant from glucose.
Give one use the plant makes of protein.
What will the gardener need to add to his crops in order to make sure they can make protein and why?
KS4 Biology /B4h / Side 1
Maximising the Rate of Photosynthesis
The Greenhouse
Look at the diagram below:
Explain how it is designed to maximise the rate of photosynthesis and the growth of the plants grown inside it.
In a modern commercial greenhouse the conditions are controlled by a computer system. Special sensors detect changes in the environment and bring about changes that make sure that the conditions are kept at the best level for photosynthesis and growth.
KS4 Biology /B4i / Side 1
How Photosynthesis Affects the Concentrations of Carbon Dioxide in Water
The following sets of apparatus were set up to show the effects that pondweed and pond snails have on their surroundings:
Tubes kept in the lightTubes kept in the dark
Bicarbonate indicator solution changes colour according to the concentration of carbon dioxide dissolved in it.
Yellow / - / When the level of carbon dioxide is highRed / - / When the level of carbon dioxide is low
Purple / - / When there is no carbon dioxide
The apparatus was left for a few days and the results recorded. Complete the table to show the change in colour of the bicarbonate indicator solution along with a reason for your answer.
Tube / Colour / Reason1 control / Red
2
3
4
5 control / Red
6
7
8
Sha Tin College / Science Department - August 05